Visual stimulus timing precision in Psychtoolbox-3: Tests, pitfalls and solutions

Visual stimulation paradigms in perception research often require accurate timing for presentation of visual stimuli. Acquisition of exact stimulus update timestamps in realtime is often crucial, both for synchronization of stimulus updates between different presentation modalities and for logging. Modern graphics hardware, multi-core processors and operating systems provide a far higher level of functionality, flexibility, and performance in terms of throughput, than systems a decade ago. They also pose new challenges for precise presentation timing or timestamping. Typical causes of interference are, eg the dynamic power management of modern graphics cards and computers, novel hybrid graphics solutions, user interface desktop composition and the properties of graphics- and CPU-scheduling of the latest generation of operating systems. This work presents results for the accuracy and robustness of visual presentation timing and timestamping tests, conducted within Psychtoolbox-3 (Kleiner et al, 2007 Perception 36 ECVP Supplement, 14) on different operating systems and graphics cards under realistic stimulus presentation loads. It explains some of the common pitfalls one can encounter when trying to achieve exact timing and some methods to avoid timing problems or reduce their severeness